Access to the social networking site Facebook has been blocked in Iran just weeks before the country's presidential elections, an Iranian news agency reported.
Iranian Labour News Agency (ILNA) reports the country's new ban on Facebook is aimed to stop supporters of reformist candidate Mir Hossein Mousavi from using the site.
Mousavi has more than 5,000 fans on his Facebook page, created for his campaign.
Mousavi, Iran's former prime minister, is seen by many as the candidate with the best chance of defeating current president, Mahmoud Ahmadinejad, a hard-liner who's often been at odds with the United States.
There has been no comment from the authorities in Tehran, the BBC reports.
Mousavi, 67, has a hard-line past and spotless revolutionary credentials appeal to conservatives. Mousavi's reformist past — he was a senior adviser to former President Mohammad Khatami who served two terms before Ahmadinejad was elected — also appeals to Iranians eager for reform.
Mousavi came to prominence after the 1979 Islamic Revolution that toppled the U.S.-backed shah.
He served briefly as foreign minister, then was prime minister from 1981-1989. His premiership spanned the destructive eight-year war with Iraq, in which at least a million people on both sides were killed.
The Associated Press contributed to this report.